The overall goal is to develop and assess the impact of standardized and generalizable simulation-based training (specific aim #1), and user interface and cognitive workflows enhancements (specific aim #2) on radiation therapy (RT) providers' performance and mental workload. Rationale: Errors in Radiation Therapy (RT) are estimated to occur in up to H 5% of the > H600,000 patients receiving RT per year in the US; with serious/lethal events occurring H 1 of 1,000-10,000 patents. The relatively high error rates and the potential for catastrophic events in RT is very concerning, and highlights underlying systematic challenges with performance and mental workload that need to be addressed. Thus, the findings from this study will have direct implications for a large number of patients. Methods: Subjects, randomized to receive (vs. not receive) simulation-based training and to 'current' vs. 'enhanced' user interfaces and cognitive workflows, will have pre- and post- assessments to quantify the impact of these interventions on a RT providers' performance and mental workload. Using a 2 x 2 balanced randomization design, we will use analysis of variance (ANOVA) to evaluate main and interaction effects from the four groups (+/-simulation-based training, and 'current' vs. 'enhanced' user interface and cognitive workflow). Research areas: Patient safety, mental workload, individual performance, simulation. Scientific disciplines: Cognitive and Behavioral Sciences; Human Factors.